Postfix discard bounces

/etc/postfix/main.cf

bounce_notice_recipient = devnull 
bounce_notice_recipient = devnull
bounce_queue_lifetime = 0d
delay_warning_time = 0h
alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases

/etc/aliases

devnull:    /dev/null

Run

newaliases
postfix reload